Problem:
"When I attach to the project the client states that there is no work for my platform or that my platform isn't supported. I've seen or been told that other people run BURP on Mac. What is going on and how do I get it working?"

Answer:
BURP does not officially support the Mac platform - especially not the powerpc variant. There are plans to maybe eventually do official builds of the client to the Mac OS X Intel series at some point in the future. Apple has stated that they plan to phase out the use of powerpc and that machines will most likely be based entirely on the Intel platform.

Warning: outdated info
A user (Dotsch) from the BURP community has made an unofficial build of the client for Macs - have a look at this thread.

Another warning: the warning is outdated
There is no longer a community build of the client for Macs.